Safety of using a 16A to 6A converter for iMac

The reply you just received does not reference any sources for its information so I would not regard it as qualified. For example, it does not provide a source for anywhere that Apple says it is not safe. I also think that the statements about damaging your home wiring and the plug and the socket are inaccurate unless your wiring is not rated for the supply you mention.

I looked up the technical specifications for one of Apple's M4 iMacs at Identify your iMac model - Apple Support

It said it has a 143W power demand. From what I could tell from a web search, India uses a 220V power supply. Your socket could supply ~1200W, so the demands of your iMac are well inside what your 6A socket could supply. You do need some safety margin but you have a large margin.

Do NOT use a 16A → 6A converter for an iMac.

It's unsafe, not recommended by Apple, and can damage the socket, the plug, or your home wiring.

Install one proper 16A socket

Incidentally you do not need a converter for amperage. I have never heard of such a thing. The amount of amps will depend upon the power demand of the device you are using.

There are converters for voltage, but Apple devices will adjust automatically (look at the specifications using the link I provided). Depending upon the source of the iMac, what you might need would be a plug/socket adapter.